The present invention relates to a power-driven screwdriver comprising:
a housing; PA1 an axially displaceable tool drive shaft, mounted rotatably in the housing, that is mounted at a first end in the housing and at its second end has a receptacle for a tool; PA1 a motor-driven drive gear, mounted rotatably on the tool drive shaft, that on the housing side is secured against axial displacement; PA1 a cam ring that is axially immobilized on the tool drive shaft and is secured against axial displacements outward; PA1 a spring element in order to preload the tool drive shaft outward toward the receptacle; PA1 first clutch elements on the drive gear; PA1 second clutch elements on the cam ring that coact with the first clutch elements in order to constitute a torque-dependent release clutch; and PA1 an adjusting device for axial adjustment of the tool drive shaft.
Screwdrivers of this kind, having an adjustable, torque-dependent shutoff clutch that generally has mutually coacting cam elements with oblique flanks, have been common for years.
An example of one such screwdriver is represented by the screwdriver marketed under the designation "ASse639" (cf. general catalog of the Applicant, "Fein Hochleistungs-Elektrowerkzeuge" 1995/96, pages 78, 79, 224).
In many situations it is desirable in this context to make the torque-dependent shutoff clutch nonfunctional, for example if the screwdriver is to be used for drilling. For this purpose, it is known to clamp the two clutch elements, which have cams with oblique entraining flanks, to one another so that torque-dependent release is prevented. This situation is referred to as "rigid through drive."
The disadvantage of a configuration of this kind is that because of the oblique cams, very large axial forces occur and must be absorbed by the bearings.
Although a variety of solutions are known in the existing art for rigidly coupling a drive shaft and an output shaft to one another (cf. U.S. Pat. Nos. 5,016,501, 3,243,023, and EP-A-0 792 723), coupling mechanisms of this kind are of complex construction and are poorly suited for use in a simple screwdriver with a torque-dependent release clutch (single-claw clutch).